Sewing machine with thread monitor

ABSTRACT

The control circuit of a catch thread device has a counter for the main shaft of the swing machine. The counter counts the number of revolutions of the main shaft 26 during the reception of one of at least two signal intensities and is reset to its initial value when this signal intensity changes to the other signal intensity. When a predetermined maximum number of revolutions is reached, the counter emits a signal indicating a thread fault.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates in general to a sewing machine and inparticular to a new and useful method and apparatus for effectingvarious sewing operations.

A thread monitor for a sewing machine, which has a counter with acounting input, a resetting input, and a presetting input for enteringcount values is known from U.S. Pat. No. 4,192,243. The pulses of apulse generator, which generates a predetermined number of pulses, whichcan be predetermined, per revolution of the main shaft, are sent to thecounting input, while a pulse generator driven by the thread pull isconnected to the resetting input.

The counter is reset to a starting value by each pulse arriving at theresetting input. Based on this value, the counter sums up the pulses onthe counter input until it is again reset by the next resetting pulse.However, when the counter has counted up to the count value set on thepresetting input before the next resetting pulse is sent, there is athread disturbance. Based on this, the counter sends a signal whichtriggers an alarm or machine stop.

Even though the needle thread can be easily monitored by a threadmonitor of such a design to detect thread end and breakage, it isstipulated in that patent that the shuttle thread on a double lockstitch sewing machine can be monitored via the needle thread bydetecting its consumption, rather than directly. Therefore, inconjunction with such a sewing machine, this thread monitor is unable torespond to disturbances on the shuttle thread rapidly and withsufficient sensitivity.

British patent specification No. 13 35 677 discloses a sewing machinewhose bobbin has a marking formed by light and dark fields on its flangefacing a light source and a light receiver. As long as thread is beingpulled off, the marking of the rotating bobbin acts as a pulsegenerator. However, the pulse sequence changes in the case of threadbreak or thread end, as a result of which the shut-off mechanism of thesewing machine is actuated via electrical or electronic means followingthe light receiver.

Due to the inertia of the bobbin, thread monitors responding to changesin the pulse sequence have the disadvantage that a reduction of thesewing machine speed brings about bobbin feed. This can cause the bobbinto stop briefly, which causes the thread monitor to respond, despitecontinued thread pull-off.

U.S. Pat. No. 3,738,296 discloses a bobbin which has a reflectivesurface. The light beams of a reserve monitoring device, which aredeflected by this surface, are sent as light signals to a counter of anexternal control circuit. The number of bobbin revolutions taking placeduring sewing is summed up in the counter, and this actual value iscompared to a preselected nominal value. The sewing machine is stoppedwhen the two values are equal.

Even though the arrangement described in the U.S. Patent Specificationmakes it possible to preselect the amount of residual thread accordingto the needs, rupture of the bobbin thread is not indicated.

SUMMARY OF THE INVENTION

It is an object of the invention to design a thread monitor of thisclass so that the thread monitor will monitor the shuttle threaddirectly for rapid and sensitive indication.

The invention provides a thread monitor which will monitor the shuttlethread directly for rapid and sensitive indication.

According to the invention, a bobbin which is held in the shuttle bodyis provided as a reflector for reflecting signals sent by a signalsending element. The bobbin includes a plurality of reflection surfaceswith different reflection characteristics. A receiving elementcooperating with the sending element to form a sensor, detects thechange in the signal which is brought about by the differences inreflection. This sensed change is sent by the sensor in the form ofpulses to the resetting input of a counter. A pre-setting input of thecounter is connected to a setting device for preselecting a maximumcount.

Because the bobbin is designed as a reflector for signals which are tobe sent from a sensing device to a sensor acting as a receiver, neitherthe sensing device nor the sensor need to be arranged in the immediatevicinity of the bobbin, which is advantageous in light of the limitedspace in the area of the shuttle.

Due to the difference in the reflection behavior of the reflectivesurfaces of the bobbin, a constant signal of the sensing device can beconverted into pulses which are sent to the resetting input of thecounter in a sequence that depends on the thread consumption.

Based on this mode of action of the bobbin, no separate pulse generatordriven by the thread pull is needed. This considerably simplifies thesubsequent installation of the thread monitor in sewing machines.

Various types of sensors can be used to monitor the rotation of thebobbin; monitoring may be performed, for example, electronically,magnetically, electrically, or pneumatically.

The count value up to which the counter sums up the pulses delivered perstitch forming cycle can be set via the presetting input of the counter.The switching operation is triggered when this count value is reached.

The count value should be selected to be as low as possible in view ofthe short reaction time until stoppage of the sewing machine. On theother hand, it should not be lower than a minimum in order to prevent abrief stoppage of the bobbin due to a short slack thread from causingmalfunction of the thread monitor. Such a stoppage is, for example, theconsequence of bobbin feed, which may occur as a result of a slightreduction of the sewing machine speed during the sewing operation.

In the case of a relatively long slack thread section after anintermediate stoppage, especially after deceleration of the sewingmachine from the maximum speed to stop, an additional counting device,by which the action of the counter of the main counting device isabolished until the maximum possible amount of slack thread is used up,is advantageous.

A relatively large amount of thread is fed during thread cutting. Onrestart, this slack thread must first be used up before the bobbin isset into rotation by repeated thread after draft. Therefore,advantageously, another additional counting device is provided, by whichthe counter of the main counting device is turned on only after thisslack thread has been used up completely.

The value of at least one additional counting device can be set by themeasure so that switching back to the counter of the main countingdevice takes place as early as possible after the slack thread has beenused up completely. However, by providing that the counter can be drivenas a function of the actual operating state of the sewing machine, whichdeviates from the sewing operation, so that a number of main shaftrevolutions associated with the operating state can be determined whichthen results in a switching over to sewing operation. One countingdevice is sufficient, which can be adjusted to the actual state of thesewing machine, such as sewing operation, intermediate stop, or threadcutting.

Whether the thread monitor according to the present invention, thethread is checked after being pulled off from the bobbin or the yarnroll by the continuous alternation of the intensity at short intervals,and the number of stitches, or the number of revolutions of the mainshaft which are to be performed prior to display after a threaddisturbance, is determined by a maximum that can be preselected. Thismaximum should be selected to be as low possible in view of the shortresponse time elapsing until the sewing machine is stopped.

A short response time is desirable, for example, when the signalgenerator has stopped as a consequence of the reduction of the frictionbetween the thread and the bobbin core at the end of the thread, but asufficient amount of thread is still present to continue the stitchformation at maximum stitch length until the number of stitchescorresponds to the maximum that can be preselected.

The maximum should advantageously not be lower than a minimal value,because a slack thread section resulting from a brief stoppage of thebobbin thus does not induce malfunction of the thread monitor. Such astoppage of the bobbin is the consequence of, e.g., a bobbin feed, whichmay occur as a result of a reduction of the sewing machine speed duringthe sewing operation. The measure according to which the number ofstitches prior to the next change is counted proved to be advantageous,because the slack thread is used up after a few stitches and the bobbinis rotated further.

The thread monitor may operate electro-optically, electromagnetically,pneumatically, or mechanically, depending on the required field ofapplication.

For example, the electro-optical monitoring process has proved to beadvantageous for thread monitoring, because the signal generator can bescanned without contact and hence without wear according to a simpletechnical solution. In addition, electro-optical thread monitors operaterelatively accurately and with a short response time.

The advantage of magnetic monitoring processes is the fact that theirfunction has proved to be particularly insensitive to dirt, and they aretherefore particularly suitable for use as thread monitors in whosesignal path the accumulation of lint generated during sewing cannot beruled out.

The use of permanent magnets at the signal generator is advantageous,because the thread monitor requires only a receiver suitable forreceiving the magnetic signals because of the permanent magnets actingas senders. If this receiver comprises a Hall sensor, it is particularlylight-weight and compact.

Other designs of the thread monitor are possible including one in whichthe proximity switch responds to inductive or capacitive signal changesand advantageously the sensor responds to pressure changes.

A larger, freely preselectable amount of residual thread to be meteredrelatively accurately is advantageous also. Such a counting device hasproved to be advantageous especially in sewing units on which largerparts are sewn.

Accordingly, it is an object of the invention to provide a threadmonitor for controlling the feed of a thread in a sewing machine inaccordance with the drive speed of the sewing machine wherein a rotatingbobbin is provided that rotates so that a sensing surface with variablesensing areas is picked up by the scanning of the sensor which has aresetting device which effects resetting after counting is done by acounting device associated therewith.

A further object of the invention is to provide a sewing machine threadmonitor which is simple in design, rugged in construction and economicalto manufacture.

A further object of the invention is to provide a method of monitoringthe operation of the sewing machine which feeds sewing thread off arotating bobbin which has a reflecting surface which is picked up by asensing device so as to send a signal to a counter and resetting device.

A further object of the invention is to provide a method of operating asewing machine which is easy to carry out and which produces a bettercontrol of the feed of a thread.

The various features of novelty which characterize the invention arepointed out with particularity in the claims annexed to and forming apart of this disclosure. For a better understanding of the invention,its operating advantages and specific objects attained by its uses,reference is made to the accompanying drawings and descriptive matter inwhich a preferred embodiment of the invention is illustrated.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings:

FIG. 1 is an axial sectional view through the shuttle of a sewingmachine constructed in accordance with the invention;

FIG. 2 is a sectional view taken along line II--II in FIG. 1;

FIG. 3 is a simplified circuit diagram of the monitoring system;

FIG. 4 is a circuit diagram of the counting device;

FIG. 5 is a sectional view through a shuttle of another embodiment ofthe invention along line V--V in FIG. 6;

FIG. 6 is a sectional view taken along line VI--VI in FIG. 5;

FIG. 7 is a diagram of the counting device associated with the sensoraccording to FIG. 5;

FIG. 8 is a sectional view through another embodiment of the shuttlealong line VIII--VIII in FIG. 9;

FIG. 9 is a sectional view along line IX--IX in FIG. 8;

FIG. 10 is a circuit diagram of the counting device associated with thesensor according to FIG. 8;

FIG. 11 is a sectional view through another embodiment of the shuttletaken along line XI--XI in FIG. 12;

FIG. 12 is sectional view taken along line XII--XII in FIG. 11;

FIG. 13 is an enlarged sectional view of a sensor according to FIG. 11;and

FIG. 14 is a diagram of the counting device associated with the sensoraccording to FIG. 11.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The shuttle drive of a first embodiment, which is shown in FIG. 1,comprises a shuttle drive shaft 1, on which a shuttle body 2, shown onlypartially, is fastened nonrotatably by a set screw 3.

A bobbin case 4 is mounted in the shuttle body 2, and the bobbin casecarries a center pin 5 that carries a bobbin 6 on which thread is wound.A bobbin 6 is provided with a front flange 7 and a rear flange 8, whichare connected by a core 9 that can be attached to the center pin 5. Onits outside, the flange 7 has a sewing surface or marking 11 formed withvariations such as light and dark fields 10.

The bobbin case 4 is designed with an opening 12 for the entry and exitof light signals. The signals are emitted by a light-emitting diode 13,which is indicated only symbolically, and are sent to a photodetector 14after being reflected on marking 10 of bobbin 11.

FIG. 3 shows, in a simplified circuit diagram, the components of acontrol circuit 15 that are needed for the function of the threadmonitor. Current flows from the positive pole of a controlled powersource via light-emitting diode 13 and a resistor 16 to ground. Currentalso flows to ground from the positive pole of the power source via thephotodetector 14, designed as a phototransistor, and a resistor 17.

A capacitor 18, which is connected via an amplifier 19 and an ANDelement 20 to an input El of a counter 2-, is connected to the emitterof the photodetector 14. Together with this counter 21, the components17 through 20 form a counting device 22.

A pulse M is sent from the output of the drive motor 24 of the sewingmachine to a negation element 23 immediately after the drive motor hasbeen turned on. The output of negation 23 is connected to the secondinput of the AND element 20.

To set the counter 21, a signal corresponding to the necessary maximumcan be sent to it via an input E2. The maximum can be preselected on acontrol panel 25, to which the input E2 is connected. A positiontransducer 27, which monitors the revolutions of the main shaft 26, isconnected to another input E3 of the counter 21. The position transducerhas a light-emitting diode 28, which is connected to the positive poleof a controlled power source, and the light-emitting diode 28 isgrounded via a resistor 29. A photodetector 30 designed as aphototransistor, is also connected to the positive pole and is groundedvia a resistor 31. A disk 32, which is mounted on the main shaft 26(nonrotatably fixed to the main shaft) and is designed with an opening33 for the passage of the light beams, is provided in the light pathbetween the light-emitting diode 28 and the photodetector 30. One pulseP is sent to the input E3 of the counter 21 on each passage.

The output A of the counter 21 is connected to an input of an ANDelement 34. Counting devices 35 through 37 are connected to the otherinputs of the AND element 34.

The counting device 35 can be driven by the pulse M sent to the outputof the drive motor 24 after each intermediate stop of the sewingmachine, while the counting device 36 receives a pulse F from a threadcutting device (not shown) after thread cutting. In contrast, thecounting device 37 can be activated by a pulse W by the sewing machineoperator actuating an appropriate switch on the sewing machine afterreplacing the empty bobbin with a full one. All three counting devices35 through 37 are connected to the position transducer 27 and receivethe pulses P sent by same.

The individual counting devices 35 through 37 are of identical design,and, as is apparent from FIG. 4, each of them has a dynamic member 41formed by a resistor 38, a capacitor 39, and an amplifier 40, aflip-flop memory 42, and a counter 43.

One input ZE1 (FIGS. 3 and 4) of each counting device 35 through 37 isconnected to the control panel 25, whereas the pulses M, F or W sent bythe sewing machine are received on input ZE2 and the pulses P arereceived on input ZE3. Output ZA of the corresponding counting device 35through 37 is connected to one input each of the AND element 34.

The dynamic member 41 is connected to the input ZE2 of the correspondingcounting device 35 through 37 and causes the pulses received M, F or Wto be present on the input S of the memory 42 for a short time only (seeFIG. 4). The other input S' of the memory 42 is connected to the outputA and the output Q' of the memory 42 is connected to the resetting inputRE of the counter 43. The output Q' is also connected to the output ZAof the counting device.

The output of the AND element 34 (FIG. 3) is connected to an OR element44, to which the counting device 37 is also connected. The output of theOR element 44 is connected via an amplifier 45 to a display member 46,which is grounded via a resistor 47. A switch 49, which is connected toa shut-off device 48 for the drive motor 24 is also connected to theoutput of the amplifier 45. The drive motor 24 drives the main shaft 26via a V-belt 50.

The first embodiment operates as follows:

During the operation of the sewing machine, the light beams of light-emitting diode 13 fall on marking 11 through the opening 12 of thebobbin case 4. The light is reflected on the marking and is sent to thephotodetector 14 after re-exiting from the opening 12. If the bobbin 6is rotated as a consequence of thread being pulled off during the sewingoperation, the light receiver 14 successively receives signals ofdifferent light intensity. However, a signal of constant light intensityis present during the stoppage of the bobbin as a consequence of threadbreak or thread end.

Only the signal generated during the transition from a darker to alighter field 10 of the marking 11 is evaluated by the control circuit15 of this embodiment. However, the thread monitor would be just asreadily able to function if only the transitions from a lighter to adarker field or both transitions were evaluated.

During each such transition, the photodetector 14 becomes conductive andcurrent flows to ground via the resistor 17.

The voltage now building up is sent to the AND element 20 via thecapacitor 18 and the amplifier 19. The capacitor 18 advantageouslyserves to filter out direct currents caused by daylight andlow-frequency alternating current caused by a light of the sewingmachine.

During sewing, the drive motor 24 sends no pulse M to the negationelement 23, so that a signal with "high" potential, hereinafter calledsignal H, is present on its output. As soon as such a signal is alsosent to the output of the amplifier 19, the counter 21 receives a signalH via its input E1 and is hereby reset into its starting position, thevalue zero. The counter 21 now starts to sum up the signals arriving atthe input E3 from the position transducer 27; each signal corresponds toone revolution of the main shaft 26 and hence to one stitch made. Aslong as the bobbin rotates, the counter 21 is repeatedly zeroed by thecorresponding signal received at the input El before the maximum set onthe, control panel 25 and preselected via the input E2 is reached. Thisvalue can be found, for example, by determining by measurement thenumber of revolutions of the main shaft 26 with full bobbin and theshortest stitch length that can be set on the sewing machine, which isneeded for rotating the bobbin 6 from one field 10 to the next.

When the bobbin 6 has stopped as a consequence of a thread disturbance,the counter 21 continues counting up to the preselected maximum andsends a signal H from its output A to the AND element 34. As will bediscussed in detail later, the counting devices 35 through 37 areconnected such that signal H is always present on their outputs ZAduring the sewing operation. The signal H of the counter 21 is thereforeable to pass through the AND element 34 unhindered. After subsequentpassage through the OR element 44 and through the amplifier 45, thesignal actuates the display device 46, and if the switch 49 is closed,at the same time also the shut-off device 48, which, depending on thedesign of the drive motor 24, either shuts the motor off immediately orprevents it from being restarted after the next stopping process.

When the drive motor 24 is actuated for the first time after stoppage ofthe sewing machine, for example, after filling the bobbin 6, the drivemotor sends pulse M to the negation element 23. As a result of this, thepotential on the output of the negation element 23 briefly changes to"low", hereinafter called signal L for short, so that signals H, whichare present on the AND element 20 and arrive from the amplifier 19, areunable to pass through.

At the same time, the pulse M is sent to the input ZE2 of the countingdevice 35 and reaches the dynamic element 41 via it. The duration of thepulse M is limited by its capacitor 39, which acts as a timing element,so that the pulse is present on the input S of the flip-flop memory 42for a short time only and sets its output Q on the signal H.

As a result of this, signal L is present on the output ZA of thecounting device 35, which output is connected to the output Q' of thememory 42, so that the AND element 34 blocks the signal and the signalsH from one of the counting devices 22, 36, and 37 are not able tointerrupt the rotation of the motor.

The resetting input RE of the counter 43 is also connected to the outputQ' of the memory 42. As soon as the signal L is present on this input,it is reset to zero and starts counting via its input P the revolutionsof the main shaft 26, until it reaches the maximum preselected via theinput ZE1. Then, via its output A, it sends a signal H to the input S'of the memory 42, as a result of which signal H will again be present onits output Q' as well as on the output ZA of the counting device 35.

The mode of operation of the counting devices 36 and 37 corresponds tothat of the counting device 35. However, the counting device 37 is to beconnected by the OR element 44 to the other counting devices 22, 35, and36, because the signal L is always present on the output ZA of thecounting device 37 during its considerably longer counting interval.

In a second embodiment, magnets 52, between which a magnet-free field 53is provided, are arranged on the outside of the flange 7 of the bobbin6. The flange acts as a signal generator 51. A receiver 54, whichresponds to changes in the magnetic field, is arranged on the front sideof the bobbin case 4. The receiver is designed as a Hall sensor 55,whose terminals FIG. 7 are connected to counting device 22 of thecontrol circuit 15. Because the magnets 52 are advantageously designedas permanent magnets, a signal emitter may be omitted.

The second arrangement operates as follows:

When thread is being pulled off from the bobbin 6, the latter isrotated, so that the Hall sensor 55 receives successively magneticsignals of varying intensity. In contrast, a magnetic signal of constantintensity is present during the stoppage of the bobbin as a consequenceof thread break or thread end. This signal is evaluated in theabove-described manner by the control circuit 15.

In a third embodiment, a receiver 56 is designed as a proximity switch57 FIGS. 8 through 10, which is connected to the counting device 22 viaan amplifier 58. The flange 7 of the bobbin 6, acts as a signalgenerator 59 and faces the proximity switch 57. The flange 7 hasprojections 60 on its outside.

Due to the projections 60, the space between the outer surface of theflange 7 and the proximity switch 57 changes continuously during therotation of the bobbin 6. As a result of this, the inductance or thecapacitance of the proximity switch 57 changes, depending on its design.These changes are evaluated in the above-described manner by the controlcircuit 15.

In another embodiment, the receiver 61 of the thread monitor is apneumatic ring beam sensor 62 (FIGS. 11 through 14), which is shown inFIG. 13 on a larger scale. The ring beam sensor 62 has a cylindricalhousing 63 with an inlet connection 64 and annular discharge nozzle 65.A tube 66, whose free end serves as an inlet opening and whose fixed endserves as a discharge connection 67, is fastened inside the housing 63.The inlet connection 64 is connected via a pressure line 68 to apressure source 69, and the discharge connection 67 is connected via apressure line 70 to a pneumatic/electrical transformer 71. The latter isconnected to the counting device 22 via an amplifier 72.

The flange 7 of the bobbin 6, acting as a signal generator 73, isprovided with projections 74 on its side facing the ring beam sensor 62.

The compressed air admitted through the inlet connection 64 is deflectedin the housing 63 and it leaves the ring beam sensor 62 through thedischarge nozzle 65. After being deflected on the flange 7, thecompressed air enters the tube 66 and leaves the ring beam sensor 62through the discharge connection 67.

Rotation of the bobbin 6 as a consequence of thread being pulled offbrings about pressure changes in the tube 66 because of the changes inthe distance between the ring beam sensor 62 and the flange 7. Thesepressure changes are transmitted to the transformer 71, which transformsthem correspondingly for evaluation in the control circuit 15.

The mode of operation of the thread monitor according to the presentinvention was explained in this embodiment on the basis of bobbin threadmonitors. However, the device is also suitable for monitoring the needlethread by arranging the signal generator rotatably in the path of theneedle thread and driving the signal generator by the needle thread.

While a specific embodiment of the invention has been shown anddescribed in detail to illustrate the application of the principles ofthe invention, it will be understood that the invention may be embodiedotherwise without departing from such principles.

We claim:
 1. A sewing machine and thread monitor arrangement, comprisinga bobbin held in a shuttle body, said bobbin having signal reflectingelements for reflecting a sensor signal; sensor means for responding tothe bobbin thread running out including means for emitting sensorsignals and means for detecting changes in signals reflected by saidelements of said bobbin in dependence upon the different reflectioncharacteristics of said elements, said sensor means generating pulsesignals; a pulse generator providing one pulse per stick forming cycle;counter means for receiving said pulse signals from said sensor; and,setting means for inputting a presetting input to said counter meansdefining a maximum count, generating a signal indicating a disturbancein the shuttle thread when said counter means reaches said maximum countat least one additional counting device, for interrupting said signalindicating a disturbance for a number of stitch cycles for using up aslack thread section after a sewing machine function that causes slackthread.
 2. Sewing machine in accordance with the claim 1, wherein saidat least one additional counting device has activation means which canbe activated after an intermediate stop, and after a pre-set number ofthe main shaft revolutions, which can be predetermined, has beenreached, and including means for sending a signal for restoring theswitching function of said counter means.
 3. Sewing machine inaccordance with claim 2, wherein at least one additional counting deviceis driven after thread cutting, and said additional counting devicesends a signal for restoring the switching function of said countermeans after a pre-set number of the main shaft revolutions, which can bepredetermined, has been reached.
 4. Sewing machine in accordance withclaim 2, wherein said preset number for the at least one additionalcounting device can be set for the consumption of slack thread sectionsof different lengths, which are caused by various machine speeds. 5.Sewing machine in accordance with claim 1, wherein said counter means isactuated as a function of the actual operating state of the sewingmachine, based on a number of main shaft revolutions associated with theoperating state which occur prior to a sewing operation.
 6. A sewingmachine with a doublelock stitch shuttle land a thread monitor,comprising: a receiver means for receiving signals of varying intensityfrom a signal generator means, said signal generating means beingconnected to a thread bobbin which is set into rotation by the threadbeing pulled off for supplying signals of different intensities to saidreceiver means during rotation, and control circuit means connected tosaid receiver means including a first counting device for counting therevolutions of a main sewing machine shaft during the duration of thereception of signals of one intensity and which is reset to its initialvalue by the change of these signals to another intensity, and forgenerating a signal indicating thread disturbance after a preselectedmaximum number of revolutions has been reached without a change ofsignal intensity to provide a switching function, at least oneadditional counting device, for interrupting said switching function fora number of stitch cycles for using up a slack thread section after asewing machine function that causes slack thread.
 7. A sewing machine inaccordance with claim 6, wherein said signal generator has asignalgenerating projection, and said signal receiver comprises aproximity switch.
 8. A sewing machine according to claim 6, wherein saidsignal generator includes air reflecting members with alternating airreflecting properties, said signal receiver means comprises a sensorincluding compressed air transmission means for directing air towardsaid signal generator and pressure sensing means that can be actuated bypressurized media for sensing changes in intensity of reflected airpressure.
 9. A sewing machine according to claim 7, wherein said controlcircuit includes an additional counting device, which can be activatedafter an intermediate stop and wherein said additional counting devicesends a signal for restoring the switching function of said firstcounting device intended for the sewing operation after a predeterminedmaximum number of revolutions of said main shaft.
 10. A sewing machinein accordance with claim 7, wherein said control circuit includes anadditional counting device, said additional counting device beingactuated after thread cutting and having means for sending a signal forrestoring the switching function of said first counting device after apredetermined maximum number of revolutions of the main shaft has beenreached.
 11. A sewing machine according to claim 7, wherein said firstcounting device of said control circuit is activated depending upon theoperating state of said sewing machine, based on a number of revolutionsof the main shaft prior to the start of sewing operations.
 12. A sewingmachine according to claim 7, wherein said control circuit means causesthe sewing machine to be stopped after a predetermined number ofrevolutions have been achieved.
 13. A sewing machine according to claim6, wherein said signal generating means includes signal-generating meansand said means for receiving signals includes a Hall sensor.